Sheet or film oblique stretching method and sheet or film clipping stretcher

ABSTRACT

Clipping both right and left side edge parts of a sheet or film by right and left pitch-variable clips having flow-directional clip pitches variable along with travel movements, respectively, having positions (AR, AL) for initiation of enlargements of flow-directional clip pitches changed between right clips and left clips, and enlarging flow-directional clip pitches along with travel movements of clips to thereby make an oblique stretch.

TECHNICAL FIELD

The present invention relates to a sheet or film oblique stretchingmethod and a sheet or film clipping stretcher, and particularly, to asheet or film oblique stretching method and a sheet or film clippingstretcher that are employable for fabrication of optical sheets or filmswith oblique orientation, such as a polarization film or phasedifference film.

BACKGROUND ART

There are techniques employing, for production with good yield such asof a polarization film or phase difference film having an orientationaxis tilted at 45 degrees, a sheet or film clipping stretcher adapted togrip right and left sides edges of a polymer film (as sheet or film) bypluralities of clips, respectively, moving those clips in a longitudinaldirection of the polymer film, giving tensile forces to the polymer filmin an oblique direction to implement an oblique stretch.

For oblique stretch by a sheet or film clipping stretcher having evenclip pitches, it is necessary to provide clips on one side with a delay(one-sided delay) identical in dimension to a stretch exit width ofclips on the other side, between sheet or film grip and releasepositions of clips, to provide a sheet or film with a stretch componentin an oblique direction tilted relative to a travel direction of thesheet or film.

In this respect, there are sheet or film clipping stretchers disclosedin patent documents 1 and 2, where they provide clip travel locuslengths between sheet or film grip and release positions of clips, witha difference between right clip and left clip to give a one-sided delay.Further, there is a sheet or film clipping stretcher disclosed in patentdocument 3, where it provides a difference between travel speed of rightclip and travel speed of left clip to give a one-sided delay.

-   Patent document 1: Japanese Patent Application Laid-Open Publication    No. 2002-86554-   Patent document 2: Japanese Patent Application Laid-Open Publication    No. 2004-325561-   Patent document 3: Japanese Patent Application Laid-Open Publication    No. 2002-22944

DISCLOSURE OF INVENTION

In the sheet or film clipping stretchers disclosed in patent documents 1and 2, there are variations caused in orientation in a transversedirection (as TD direction) of sheet or film due to the differencebetween right and left clip travel locus lengths, in addition to unevenvariations in distance between right and left opposing clips,constituting a difficulty of stable production, of high-quality obliquestretched sheet or film.

Further, in the sheet or film clipping stretcher disclosed in patentdocument 1, there is an angle of 45 degrees provided between stretchinlet and stretch outlet constituting a disadvantage in equipmentlayout. Further, upon fine adjustment of tilt angle, it is required tochange not simply angles of the stretcher, but also layouts of upstreamand downstream associated equipments of the stretcher.

Further, in the sheet or film clipping stretcher disclosed in patentdocument 3, it is needed to make a grip of (clip on) sheet or film byclips, simultaneously starting a stretch, and release (clip off) sheetor film from the grip by clips, simultaneously with a completion ofstretch, in addition to that upon clip-on and clip-off, travel speeds ofclips are different between right and left, causing sheet or film gripsto be uneven between right and left, actually constituting a difficultyof stable production. Further, magnification ratios in a flow direction(as MD direction) become different between right and left.

It is an object of the present invention to solve the problemsdescribed, allowing for implementation of a stable production ofhigh-quality oblique stretched sheet or film.

According to a first aspect of the present invention, a sheet or filmoblique stretching method comprises clipping moving-directionally rightand left side edge parts of a sheet or film by first and second cliparrays composed of pitch-variable clips having clip pitches in a movingdirection of the sheet or film variable along with travel movementsthereof, having, with respect to the moving direction of the sheet orfilm, a position for the first clip array to initiate enlargement ofclip pitch thereof changed from a position for the second clip array toinitiate enlargement of clip pitch thereof, and enlarging clip pitchesof the first and second clip arrays along with travel movements of thefirst and second clip arrays to thereby make an oblique stretch of thesheet or film.

According to a second aspect of the present invention, a sheet or filmoblique stretching method comprises clipping moving-directionally rightand left side edge parts of a sheet or film by first and second cliparrays composed of pitch-variable clips having clip pitches in a movingdirection of the sheet or film variable along with travel movementsthereof, having, with respect to the moving direction of the sheet orfilm, a factor of enlargement of clip pitch of the first clip arrayalong with travel movement of the first clip array changed from a factorof enlargement of clip pitch of the second clip array along with travelmovement of the second clip array, and enlarging clip pitches of thefirst and second clip arrays along with travel movements of the firstand second clip arrays to thereby make an oblique stretch of the sheetor film.

According to a third aspect of the present invention, a sheet or filmclipping stretcher comprises first and second clip arrays composed ofpitch-variable clips having clip pitches in a moving direction of asheet or film variable along with travel movements thereof, andconfigured to clip moving-directionally right and left side edge partsof the sheet or film, and first and second clip array circulatorsline-symmetrically arranged on a plane, and configured to circulate thefirst and second clip arrays along prescribed routes, respectively, theprescribed routes being routes having, with respect to the movingdirection of the sheet or film, a position for the first clip array toinitiate enlargement of clip pitch thereof changed from a position forthe second clip array to initiate enlargement of clip pitch thereof.

According to a fourth aspect of the present invention, a sheet or filmclipping stretcher comprises first and second clip arrays composed ofpitch-variable clips having clip pitches in a moving direction of asheet or film variable along with travel movements thereof, andconfigured to clip moving-directionally right and left side edge partsof the sheet or film, and first and second clip array circulatorsline-symmetrically arranged on a plane, and configured to circulate thefirst and second clip arrays along prescribed routes, respectively, theprescribed routes having, with respect to the moving direction of thesheet or film, an interval for a factor of enlargement of clip pitch ofthe first clip array along with travel movement of the first clip arrayto be changed from a factor of enlargement of clip pitch of the secondclip array along with travel movement of the second clip array.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an entire configuration of a sheet or filmclipping stretcher according to an embodiment of the present invention.

FIG. 2 is a plan view of essential parts of the sheet or film clippingstretcher in a minimal pitch state according to the embodiment.

FIG. 3 is a plan view of essential parts of the sheet or film clippingstretcher in a maximal pitch state according to the embodiment.

FIG. 4 is a side view of essential parts of the sheet or film clippingstretcher in the minimal pitch state according to the embodiment.

FIG. 5 is a side view of essential parts of the sheet or film clippingstretcher in the maximal pitch state according to the embodiment.

FIG. 6 is a plan of entirety illustrating an oblique stretch by sheet orfilm clipping stretcher according to an embodiment of the presentinvention.

FIG. 7 is a plan of entirety illustrating an oblique stretch by sheet orfilm clipping stretcher according to another embodiment of the presentinvention.

FIG. 8 is a plan of entirety illustrating an oblique stretch by sheet orfilm clipping stretcher according to another embodiment of the presentinvention.

FIG. 9 is a plan of entirety illustrating an oblique stretch by, sheetor film clipping stretcher according to still another embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

There will be described an embodiment of a sheet or film clippingstretcher according, to the present invention, with reference to FIG. 1to FIG. 5.

Description is now made of an entire configuration of a sheet or filmclipping stretcher according to the present embodiment with reference toFIG. 1.

The sheet or film clipping stretcher 200 includes endless loops 10R and10L that have multiplicities of clips 20 configured to clip a sheet orfilm. The endless loops 10R and 10L are arranged to be line-symmetricabout a line CL on a plane as illustrated in FIG. 1, which line can beset arbitrarily on the plane. It is noted that in view of an inlet endof sheet or film S (the left end in FIG. 1), that endless loop residingon the right side is referred herein to the endless loop 10R, and thatendless loop residing on the left side, to the endless loop 10L.

The endless loops 10R and 10L have their sets of clips 20 guided byreference rails 100 to circulate in a looping manner. As illustrated inFIG. 1, for endless loop 10R, the circulation is clockwise, and forendless Loop 10L, the circulation is counterclockwise.

A preheating zone A, a stretching zone B, and a heat-treating zone C areconfigured in this order from the inlet end of sheet or film S to anoutlet end (the right end in FIG. 1).

It is noted that in FIG. 1, designated by a quadrilateral U1 is part ofsheet or film S before its transverse stretch (that is, in thepreheating zone A). And, quadrilaterals U2 and U3 depict how thequadrilateral U1 is deformed, when passing through the stretching zone B(in flow-directional and transverse stretch) and the heat-treating zoneC (after flow-directional and transverse stretch), respectively.

It is now assumed that the quadrilateral U1 has a transverse (TD)dimension W₀ identical to a transverse size of sheet or film S, and thequadrilateral U3 has a transverse (TD) dimension W₁ identical to atransverse size of sheet or film S after flow-directional and transversestretch. Further, the quadrilateral U1 has a flow-directional (MD)dimension L₀, which is assumed to develop to L₁ after flow-directionaland transverse stretch (that is, in the quadrilateral U3). By suchsettings, it so follows that, as the quadrilateral U1 passes through thestretching zone B, this quadrilateral U1 (that is, the quadrilateral U2)has a transverse dimension W, and a flow-directional dimension L,meeting inequality expressions, such that W₀≦W≦W₁, and L₀≦L≦L₁,respectively.

There will be describe below stretching sheet or film S under such theassumption, and by applying dimensions of quadrilaterals U1, U2, and U3to description of flow-directional and transverse sizes of sheet or filmS, for easier comprehension.

In the preheating zone A, the endless loops 10R and 10L have a spacingdistance D_(T) corresponding to a transverse width W₀ of sheet or film Sbefore transverse stretch, and the endless loops 10R and 10L arearranged in parallel with the width W₀ kept as it is over the entireregion.

In the stretching zone B, the endless loops 10R and 10L have a graduallyincreased spacing distance D_(T), as they extend from the preheatingzone A toward the heat-treating zone C, while the endless loops 10R and10L are subject to a non-parallel arrangement. For the endless loops 10Rand 10L in the stretching zone B, the spacing distance D_(T) is varied,becoming correspondent to the transverse width W₀ of sheet or film Sbefore transverse stretch at a stretch initiating end (as a connectedend to the preheating zone A), and correspondent to a transverse widthW₁ of sheet or film S stretched transversely finally at a stretchcompleting end (as a connected end to the heat-treating zone C).

In the heat-treating zone C, the endless loops 10R and 10L have aspacing distance corresponding to the transverse width W₁ of sheet orfilm S stretched transversely finally, and the endless loops 10R and 10Lare arranged in parallel, with the width W₁ kept as it is over theentire region.

Description is now made of details of configuration of the sheet or filmclipping stretcher 200 according to the present embodiment, withreference to FIG. 2 to FIG. 5.

The right and left endless loops 10R and 10L each have a number of clips20, of which a respective one is mounted on one longitudinal end part(at the front) of a clip support member 30 rectangular in shape. It isnoted that for each of clips 20 of the right endless loop 10R (as clipson the right side) and clips 20 of the left endless loop 10L (as clipson the left side), employed is a pitch-variable type adapted for aflow-directional clip pitch (as clip MD pitch) to be variable along withmovement by travel.

The clip 20 is configured for a clipping of sheet or film S in areleasably gripping manner, with a yoke-shaped clip body 21, astationary lower clip member 22 fixedly attached to the clip body 21, amovable lever 24 rotatably attached to the clip body 21 by a pin 23, anda movable upper clip member 26 swingably attached to a lower end of themovable lever 24 by a pin 25. And, the clip 20 is adapted to clip a sideedge of sheet or film S in a pinching manner by combination of thestationary lower clip member 22, and the movable upper clip member 26.

For the number of clips 20, there is a set of clip support members 30identical in number thereto, of which a respective one is adapted toindividually support a clip 20. The clip support member 30 is configuredas a rigid frame structure enclosed in a section (refer to FIG. 4 andFIG. 5) with a front wall 37, a rear wall 38, an upper beam 35, and alower beam 36. At both ends (the front wall, 37 and the rear wall 38) ofthe clip support-member 30, there are travel wheels 33 and 34 rotatablysupported by axles 31 and 32, respectively. The travel wheels 33 and 34are adapted to roll on horizontal travel roadbeds 111 and 112 formed ona base 110. The travel roadbeds 111 and 112 are parallel to a referencerail 110, along the length.

At far end sides (read sides) of the upper beam 35 and the lower beam 36of each clip support member 30, there are longitudinal elongate holes(as elongate bores) 39 formed therein. The upper and lower elongateholes 39 have sliders 40 respectively engaged therewith and slidable inlongitudinal directions of the elongate holes 39.

In a vicinity of one end part (on the clip 20 side) of each clip supportmember 30, there is a single first shaft member 51 vertically providedthrough the upper beam 35 and the lower beam 36. The upper and lowersliders 40 of each clip support member 30 have a single second shaftmember 52 vertically provided therethrough.

To the first shaft member 51 of each clip support member 30, one end ofa main link member 53 is pivotally connected. The other end of the mainlink member 53 is pivotally connected to the second shaft member 52 of aneighboring clip support member 30.

To the first shaft member 51 of each clip support member 30, one end ofa sub-link member 54 is pivotally connected, in addition to the mainlink member 53. The sub-link member 54 is pivotally connected at theother end to an intermediate part of the main link member 53, by a pivotshaft 55.

Main link members 53 and sub-link members 54 constitute linkages,whereby as illustrated in FIG. 2, the farther their sliders 40 go towardthe far ends of clip support members 30 (opposite to the clips) thesmaller those pitches (clip MD pitches) D_(M) that neighboring clipsupport members 30 have therebetween become, and as illustrated in FIG.3, the more their sliders 40 come up toward the one ends of clip supportmembers 30 (toward the clips) the greater those pitches D_(M) thatneighboring clip support members 30 have therebetween become.

It is noted that in the present embodiment, neighboring clip supportmembers 30 have a minimal pitch D_(M)(MIN) therebetween established bythe neighboring clip support members 30 contacting each other, asillustrated in FIG. 2, and neighboring clip support members 30 have amaximal pitch D_(M)(MAX) therebetween established by sliders 40 arrivingat stroke end parts at the one end sides (the clip sides) of the clipsupport members 30.

The first shaft member 51 has guide rollers (as engaging elements) 56rotatably provided on a lower end thereof. The guide rollers 56 areengaged with a recessed channel 101 of the reference rail 100 providedon the base 110 to define a circulation route of clips 20. The firstshaft member 51 has a driving roller 58 rotatably provided on an upperend thereof.

The driving, roller 58 is configured to engage with drive sprockets 11and 12 (refer to FIG. 1) in a selective manner to have a respective clipsupport member 30 travel along the circulation route. In other words,the drive sprockets 11 and 12 are adapted to selectively engage with thedriving roller 58 of a respective clip support member 30, and are drivento rotate by electric motors 13 and 14 (refer to FIG. 1) to provide eachclip support member 30 with forces to have the clip support member 30travel along the circulation route.

The second shaft member 52 has pitch setting rollers (as engagingelements) 57 rotatably provided on a lower end thereof. The pitchsetting rollers 57 are engaged with a recessed channel 121 of a pitchsetting rail 120 provided on the base 110, along with the reference rail100, for the sliders 40 to be set in position in the elongate holes 39.

The pitch setting rail 120 works for sliders 40 to be set in position inelongate holes 39 depending on a spacing distance P thereof relative tothe reference rail 100, to thereby set pitches D_(M) between neighboringclip support members 30 in a variable manner. By the pitch setting rail120, the longer the spacing distance P relative to the reference rail100 becomes (that is, the farther it is spaced off the reference rail100) the farther sliders 40 are forced to go toward the far ends of clipsupport members 30 (opposite to the clips), rendering the smallerpitches D_(M) between neighboring clip support members 30, and theshorter the spacing distance P relative to the reference rail 100becomes (that is, the nearer it comes up to the reference rail 100) themore sliders 40 are forced to come up toward the one ends of clipsupport members 30 (toward the clips), rendering the greater pitchesD_(M) between neighboring clip support members 30.

Description is now made of the pitch setting rail 120, with reference toFIG. 4 and FIG. 5. In the preheating zone A, as illustrated in FIG. 4,the spacing distance P between pitch setting rail 120 and reference rail100 is set to a maximal value (P (MAX)) over the entire region. In thissituation, between neighboring clip support members 30, the pitch D_(M)is set to a minimal value D_(M)(MIN).

In the stretching zone B, the spacing distanced between pitch settingrail 120 and reference rail 100 gradually becomes shorter, as theyextend from the stretch initiating end (as the connected end to thepreheating zone A), where it has, the maximal value (P (MAX)), to thestretch completing end, where it has a minimal value P (MIN).

In the heat-treating zone C, as illustrated in FIG. 5, the spacingdistance P between pitch setting rail 120 and reference rail 100 is setto the minimal value (P (MIN)) over the entire region. In thissituation, between neighboring clip support members 30, the pitch D_(M)is set to a maximal value D_(M)(MAX).

Description is now made of functions of the sheet or film clippingstretcher 200 according to the present embodiment.

For the right endless loop 10R, the drive sprockets 11 and 12 are drivento rotate clockwise by the electric motors 13 and 14, and for the leftendless loop 10L, the drive sprockets 11 and 12 are driven to rotatecounterclockwise by the electric motors 13 and 14. And, those clipsupport members 30 of which driving rollers 58 are engaged with thedrive sprockets 11 and 12 are given forces to travel. The endless loop10R is thereby forced to go round clockwise, and the endless loop 10L,to go round counterclockwise, whereby sheet or film S is taken inbetween the endless loops 10R and 10L at the left end in FIG. 1.

At an opening for sheet or film S to be taken in, both side edges ofsheet or film are clipped (clip on) by clips 20 of the endless loops 10Rand 10L, and the sheet or film S first enters the preheating zone A, asthe endless loops 10R and 10L move, that is, as clip support members 30are guided to travel by reference rails 100.

In the preheating zone A, the spacing, distance DT between endless loops10R and 10L is kept as it is correspondent to a transverse width W₀before transverse stretch, the endless-loops 10R and 10L being arrangedparallel to each other over the entire region. And, the spacing distanceP between pitch setting rail 120 and reference rail 100 is set to amaximal value P (MAX) uniformly over the entire region. Accordingly, inthe preheating zone A, simply a preheating is performed, and neitherflow-directional stretch nor transverse stretch of sheet or film S isperformed.

Next, the sheet or film S enters the stretching zone B. In thestretching zone B, the endless loops 10R and 10L have a graduallyincreasing spacing distance D_(T), as they move from the preheating zoneA toward the heat-treating zone C. Further, the spacing distance Pbetween pitch setting rail 120 and reference rail 100 becomes graduallyshorter (P (MAX)→P (MIN)), as they extend from the preheating zone Atoward the heat-treating zone C. Accordingly, sliders 40 are displacedtoward the one ends (toward clips) of clip support members 30, havinggradually increased pitches D_(M) between neighboring clip supportmembers 30. By that, in the stretching zone B, both flow-directionalstretch and transverse stretch of sheet or film S are performedsimultaneously.

After that, the sheet or film S enters the heat-treating zone C. In theheat-treating zone C, the spacing distance D_(T) between endless loops10R and 10L is kept as it is correspondent to a transverse width W₁after transverse stretch, the endless loops 10R and 10L being arrangedparallel to each other over the entire region. And, the spacing distanceP between pitch setting rail 120 and reference rail 100 is set to aminimal value P (N) uniformly over the entire region. Accordingly, inthe heat-treating zone C, simply a heat treatment such as temperaturecontrol is performed, and neither flow-directional stretch nortransverse stretch of sheet or film S is performed.

At an outlet of the heat-treating zone C, the sheet or film is released(clip off) from the clipping by clips 20 of the endless loops 10R and10L, and, the sheet or film goes straight ahead, while clip supportmembers 30 are guided by reference rails 30 to circulate in a loopingmanner.

For an oblique stretch to be made, as illustrated in FIG. 6, there isgiven a difference ΔL in the moving direction of sheet or film between aposition AR set for clips 20 of the right endless loop 10R to initiatean enlargement of the flow-directional clip pitch and a position AL setfor clips 20 of the left endless loop 10L to initiate an enlargement ofthe flow-directional clip pitch.

It is now assumed that for the oblique stretch to be at an angle (asorientation angle) of 45 degrees, the difference ΔL is given such thatΔL=(film width at stretch outlet)×(flow-directional clip pitch ininitial phase before stretch)/{(flow-directional clip pitch uponcompletion of stretch)−(flow-directional clip pitch in initial phasebefore stretch)}.

By that, subject to a uniform speed driving of the right and leftendless loops 10R and 10L, the flow-directional clip pitches increase asclips 20 travel to move, thereby making a flow-directional stretch,while effecting an oblique stretch.

It is noted that there are set identical values to a distance betweenthe position AR for clips 20 of the right endless loop 10R to initiatean enlargement of flow-directional clip pitch and a position BR tocomplete the enlargement, and a distance between the position AL forclips 20 of the left endless loop 10L to initiate an enlargement offlow-directional clip pitch and a position BL to complete theenlargement.

It is thereby permitted to make an oblique stretch without differencesdeveloped between, among others, travel locus lengths or travel speedsof right and left clips 20, thus allowing even for a sheet or filmclipping stretcher of straight-going type to implement stable productionof a high-quality oblique stretched sheet or film without causing, amongothers, variations in orientation in a transverse direction (as TDdirection) of sheet or film.

In particular, at the time of clip-on, right and left clips 20 have aneven travel speed, and at the time of clip-off also, right and leftclips 20 have an even travel sped whereby the gripping as well as thereleasing of sheet or film is kept free of variations between right andleft. By this also, it is allowed to implement stable production of ahigh-quality oblique stretched sheet or film.

Further, between the right and left endless loops 10R and 10L, theiramounts of enlargement of flow-directional clip pitch of clips 20 maywell be equalized to each other. It is thereby permitted to produce ahigh-quality oblique stretched sheet or film with even right and leftstretch ratios. Further, the magnification of oblique stretch can beadjusted by setting enlargement amounts of clip pitches.

The enlargement amounts of clip pitches can be set arbitrarily byconfiguration of pitch setting rails 120, thus allowing for facile andflexible implementations of, among, others, production of a high-qualityoblique stretched sheet or film with even right and left stretch ratios,and adjustment of the magnification of oblique stretch.

Further, in the present embodiment, together with, the oblique stretchdescribed, a transverse stretch is made between positions ER and EL forinitiation of a transverse stretch and positions FR and FL forcompletion of the transverse stretch on the right and left endless loops10R and 10L. It is thereby enabled to produce an oblique stretched sheetor film as transversely stretched, with good productivity.

In the present embodiment, the right and left endless loops 10R and 10Lhave their positions ER and EL for transverse stretch initiation andpositions FR and FL for transverse stretch completion on locationsidentical to each other with respect to the moving direction of sheet orfilm, whereas like an embodiment illustrate in FIG. 7, positions ER andEL for transverse stretch initiation and positions FR and FL fortransverse stretch completion of right and left endless loops 10R and10L may be set apart from each other respectively by an equivalentdifference ΔL in a moving direction of sheet or film, to that between aposition AR for initiation of flow-directional clip pitch enlargement ofclips 20 of the right endless loop 10R and a position AL for initiationof flow-directional clip pitch enlargement of clips 20 of the leftendless loop 10L.

In this case, the right and left endless loops 10R and 10L have aninterval for oblique stretch (as interval for flow-directional stretch)and an interval for transverse stretch identical to each other in themoving direction of sheet or film.

For elimination of transverse stretch, like an embodiment illustrated inFIG. 8, there may be simply given a difference ΔL in a moving directionof sheet or film between a position AR for initiation offlow-directional clip pitch enlargement of clips 20 of a right endlessloop 10R and a position AL for initiation of flow-directional clip pitchenlargement of clips 20 of a left endless loop 10L.

It is noted that this case may also be subject to a uniform speeddriving of the right and left endless loops 10R and 10L, and havemutually identical values set to a distance between the position AR forclips 20 of the right endless loop 10R to initiate an enlargement offlow-directional clip pitch and a position BR to complete theenlargement, and a distance between the position AL for clips 20 of theleft endless loop 10L to initiate an enlargement of flow-directionalclip pitch and a position BL to complete the enlargement.

Description is now made of another embodiment for oblique stretch, withreference to FIG. 9. This embodiment has different factors ofenlargement set for flow-directional clip pitches of clips 20 (asamounts of enlargement in flow-directional clip pitch per unit amount ofmovement), between the right endless loop 10R and the left endless loop10L. In this embodiment, the right endless loop 10R has a factor ofenlargement of flow-directional clip pitch greater than a factor ofenlargement of flow-directional clip pitch of the left endless loop 10L.

Such being the case, between right endless loop 10R and left endlessloop 10L, enlargement factors of flow-directional clip pitches of clips20 are changed, whereby also an oblique stretch can be implemented.

This embodiment may well be subject to a uniform speed driving of theright and left endless loops 10R and 10L and have mutually identicallocations set in a moving direction of sheet or film, to a position ARfor clips 20 of the right endless loop 10R to initiate an enlargement offlow-directional clip pitch, and a position AL for clips 20 of the leftendless loop 10L to initiate an enlargement of flow-directional clippitch.

For production of an oblique stretched sheet or film with, equalizedright and left stretch ratios under that setting, as it is desirable,there may well be a distance set between the position AR for clips 20 ofthe right endless loop 10R to initiate an enlargement offlow-directional clip pitch and a position BR to complete theenlargement, to be longer than a distance between the position AL forclips 20 of the left endless loop 10L to initiate an enlargement offlow-directional clip pitch and a position BL to complete theenlargement, in order for flow-directional clip pitches of right andleft clips 20 to have equalized values upon completion offlow-directional stretch.

This embodiment also permits an oblique stretch to be made withoutdeveloped differences between travel locus lengths of right and leftclips 20, thus allowing even for a sheet or film stretcher ofstraight-going type to implement stable production of a high-qualityoblique stretched sheet or film without causing, among others,variations in orientation in a transverse direction (as TD direction) ofsheet or film. Further, at the time of clip-on, right and left clips 20have an even travel speed, and at the time of clip-off also, right andleft clips 20 have an even travel speed, whereby the gripping as well asthe releasing of sheet or film is kept free of variations between rightand left. By this also, it is allowed to implement stable production ofa high-quality oblique stretched sheet or film.

It is noted that in this embodiment also, like transverse stretch to theembodiment illustrated in FIG. 6 or FIG. 7 may well be made together,and further, for an oblique stretch to be made, there may well be acombination with a difference given in a moving direction of sheet orfilm between positions for clips 20 to initiate enlargement of flowdirectional clip pitch in right clips 20 and left clips 20.

INDUSTRIAL APPLICABILITY

As will be seen from the foregoing description, according to the presentinvention, in a sheet or film oblique stretching method,flow-directional clip pitches are enlarged along with travel movementsto thereby perform a flow-directional stretch, while having positionsset for initiation of enlargement of the flow-directional clip pitchesto be different in a moving direction of sheet or film between rightclips and left clips, or having different ratios of enlargement inflow-directional clip pitches of right and left clips, to thereby makean oblique stretch, thus allowing for implementation of an obliquestretch without developed differences between travel locus lengths ofright and left clips.

Further, upon a clip-on for sheet or film to be gripped as well as upona clip-off for sheet or film to be released, travel speeds of clips canbe equalized, thus permitting the gripping of sheet or film to be keptfree of variations between right and left. By those matters, it isallowed to implement stable production of a high-quality obliquestretched sheet or film.

It is thereby allowed even for a sheet or film stretcher ofstraight-going type to implement stable production of a high-qualityoblique stretched sheet or film without causing variations inorientation in a transverse direction (as TD direction) of sheet orfilm.

Further, variation amounts of flow-directional clip pitches of clips canbe set to thereby adjust the magnification of an oblique stretch,allowing in addition for a transverse stretch to be effectedsimultaneously with the oblique stretch.

The invention claimed is:
 1. A sheet or film oblique stretching methodcomprising: feeding a sheet or film to a preheating zone, a stretchingzone and a heat-treating zone while keeping opposite side edge parts ofthe sheet or film clipped by first and second clip arrays composed ofpitch-variable clips having clip pitches, each pitch being a distancebetween adjacent clips, in a moving direction of the sheet or film, thepitches being variable in the moving direction of the sheet or film;having, with respect to the moving direction of the sheet or film, aposition for the first clip array to initiate enlargement of clip pitchdifferent from a position for the second clip array to initiateenlargement of clip pitch in the stretching zone; and enlarging clippitches of the first and second clip arrays along with the travel of thefirst and second clip arrays to thereby make an oblique stretch of thesheet or film in the stretching zone.
 2. A sheet or film obliquestretching method comprising: feeding a sheet or film to a preheatingzone, a stretching zone and a heat-treating zone while keeping oppositeside edge parts of the sheet or film clipped by first and second cliparrays composed of pitch-variable clips having clip pitches, each pitchbeing a distance between adjacent clips, in a moving direction of thesheet or film, the pitches being variable in the moving direction of thesheet or film; having, with respect to the moving direction of the sheetor, film, a factor of enlargement of clip pitch of the first clip arrayalong the travel of the first clip array different from a factor ofenlargement of clip pitch of the second clip array along with the travelof the second clip array in the stretching zone; and enlarging clippitches of the first and second clip arrays along the travel of thefirst and second clip arrays to thereby make an oblique stretch of thesheet or film in the stretching zone.
 3. The sheet or film obliquestretching method according to claim 1, comprising enlarging a spacingbetween the first and second clip arrays along with the travel of thefirst and second clip arrays, to thereby make a transverse stretch ofthe sheet of film together with the oblique stretch.
 4. The sheet orfilm oblique stretching method according to claim 2, comprisingenlarging a spacing between the first and second clip arrays along withthe travel of the first and second clip arrays, to thereby make atransverse stretch of the sheet of film together with the obliquestretch.
 5. The sheet or film oblique stretching method according toclaim 1, wherein the first and second clip arrays travel at a uniformspeed at a time of clip-on in the preheating zone and at a time of clipoff in the heat-treating zone.
 6. The sheet or film oblique stretchingmethod according to claim 2, wherein the first and second clip arraystravel at a uniform speed at a time of clip-on in the preheating zoneand at a time of clip off in the heat-treating zone.